It always makes me cringe when I hear about friends getting fleeced buying spare/extra BlackBerry chargers from carrier stores. Carriers tend to charge you upwards of $20 for the convenience of picking up a charger in store. A bit back I mentioned that you could pick up a older MiniUSB charger on eBay for ~$3 but original MicroUSB chargers made by RIM were going for $6.50+.
I was in the market to pick up some spare MicroUSB chargers to have for travelling, office, and around my apartment so I did some digging. While the price of an original OEM BlackBerry charger is still about $6 with free shipping on Amazon you can pick up a international version of the charger for $2.95 with free shipping on eBay. You can find them at this link or this link from Mobile Liquidations (Large Seller with over 29,000 transactions).
I picked up 6 of them and they work as advertised. The cool part is that unlike the regular BlackBerry charger the International version comes with replaceable plugs so you can use it around the world. This makes it a little bit bulkier but it weighs the same.
Let me know if you find any better deals on BlackBerry chargers!